Where Does the Rest of the Voltage Go in a Rectifier?

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Discussion Overview

The discussion revolves around the voltage readings from a rectifier rated at 12V, where participants explore the reasons for a measured output of 4.5V. The conversation includes considerations of voltage drop, current drawn by the load, and the effects of filtering capacitors on voltage measurements.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions whether the discrepancy in voltage readings is due to voltage drop or the current drawn by the load.
  • Another participant suggests measuring the voltage on the other side of the rectifier with the voltmeter set to AC to gather more information.
  • A participant notes that voltmeters apply a light load and implies that the low voltage reading may be due to another issue rather than the voltmeter itself.
  • It is proposed that without a filter capacitor, the output of the rectifier remains AC, and the measured voltage is a DC component of a varying waveform.
  • Participants recommend adding a filter capacitor to stabilize the voltage and suggest measuring AC voltage to verify the setup.
  • There is a caution against using an ohmmeter on a live power supply, with clarification that a multimeter should be used instead.

Areas of Agreement / Disagreement

Participants express uncertainty regarding the cause of the low voltage readings, with multiple competing views on whether it is due to voltage drop, current draw, or the absence of a filter capacitor. The discussion remains unresolved.

Contextual Notes

Participants mention the importance of measuring AC voltage and the potential inaccuracies of DC measurements without a filter capacitor, indicating limitations in the current understanding of the circuit behavior.

sportynumair
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When we take down voltmeter readings from the terminals of a Rectifier (rated 12V), we get the voltmeter reading as 4.5V. Does that mean the rest of the voltage is lost in the form of voltage drop? or is it because of the current drawn by the load? I would be glad if someone could please post the answer.

Thanks.
Numair
 
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If you measure the voltage on the other side of the rectifier, with the voltmeter set to AC, what voltage do you read?
 
its coming out as 4.5Volts...so i want to know if the rest of the voltage is lost in voltage drop? or is it because of the current that the load on the secondary that is withdrawing. thanks
 
Voltmeters put a very, very light load on the voltage being measured so no I don't think the voltmeter is loading the power supply. It's much more likely there's some other problem causing low voltage.
 
If you don't have a filter cap, the output of the rectifiers is still AC( well, call it varying DC like you turn the negative half of the sine wave around and become like lumpy waveform), you are measuring the DC component of the rectified lumpy voltage. Put a 22 to 100 uF cap across the output and you should get the voltage.

If not, then read the AC voltages to make sure you have everything hooked up correctly.
 
yungman said:
If you don't have a filter cap, the output of the rectifiers is still AC( well, call it varying DC like you turn the negative half of the sine wave around and become like lumpy waveform), you are measuring the DC component of the rectified lumpy voltage. Put a 22 to 100 uF cap across the output and you should get the voltage.

If not, then read the AC voltages to make sure you have everything hooked up correctly.

Thanks...but i want to know the loss in voltage is because of voltage drop? or is it because of the current drawn by the load?
 
sportynumair said:
Thanks...but i want to know the loss in voltage is because of voltage drop? or is it because of the current drawn by the load?

Post a sketch of your circuit, with the AC and DC DVM readings you measured...
 
sportynumair said:
Thanks...but i want to know the loss in voltage is because of voltage drop? or is it because of the current drawn by the load?

If you measure with just a multimeter, there is very little current drawn. If you don't have a filter cap, it is not accurate. To verify what I said, put your multimeter in AC Volt and measure, you should see AC voltage across the output of the rectifier. This is the AC I am talking about and this is the part that you miss when you measure with a DC Volt setting. As I said, without the filter, the output has a lot of ripple and it mess up your reading.
 
Last edited:
If you measure with just a ohmmeter,

Do not make measurements in a live power supply with an ohmmeter - even a Fluke.
 
Last edited:
  • #10
Studiot said:
Do not make measurements in a live power supply with an ohmmeter - even a Fluke.

No, I should say multi meter, not a meter set in ohm! That would be bad! I changed the post already.
 

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